1. Field of the Invention.
The present invention relates to control valves capable of handling the flow of solid and semi-solid material which is erosive or corrosive in nature such as valves used in handling cold slurries such as in liquefaction or gasification, processes handling raw shale such as the extraction of shale oil, and for handling similar materials such as catalysts used in refining crude oil.
2. Description of the prior art.
Numerous designs of valves (such as slide valves) have been suggested and used for controlling solids flow. The following U.S. Patents are directed to such valves: U.S. Pat. Nos. 132,974; 2,787,438; 3,307,574; 3,701,359; 3,976,094; 4,253,487; 3,842,861; 3,964,507; 4,316,483; 4,331,316; and 4,531,539.
Various problems have been encountered with the prior art valves. In valves in which bolts are used which are exposed to hot material, i.e., in which gate guides are bolted to a valve body and in which an orifice plate is bolted to the body, difficulties are encountered in maintenance because of the bolts' tendency to lock-up after exposure to hot material. Often such bolts need to be cut out. Load carrying bolts which are changed or distorted can result in stretching, changed clearances and in parts which are thus released and fall through the valve. Many bolts used in such applications are made from expensive alloys which are also expensive to work with. Many valves require purging to to keep guides free of catalyst buildup; but frequent purging eats away parts of the guides and gates (or discs). Often guides for gates or discs are restrained such as by being welded to an orifice plate or bolted to an orifice plate or a side of a valve body. Such restraint prevents the guides from "growing" as the temperature increases